The present invention relates to a print head having an array of printing elements such as nozzle array of an ink jet printer, and more particularly, to an elongated print head capable of providing a relatively wide band like imaging area upon a single scanning with respect to an image recording sheet. The present invention also relates to such print head for a multiple color ink jet printer capable of proving the relatively wide band like imaging area of multiple colors.
In a conventional serial scanning type ink jet printer for printing image on a continuous sheet, a band like image for one line is formed of a plurality of main scanning lines by moving the print head in a main scanning direction while ejecting ink therefrom, the main scanning direction being a lateral direction, i.e., widthwise direction of the continuous sheet, perpendicular to an auxiliary scanning direction, i.e., roll-out direction thereof. Then, the recording sheet is fed by a predetermined amount in the auxiliary scanning direction, and thereafter, the band like image for the next line is printed upon main scanning motion of the print head. By repeatedly performing the main scanning and auxiliary scanning motions, an image is formed on the sheet.
In case of a conventional color ink jet printer, also, a band like color image for one line is formed while ejecting inks of different colors such as cyan magenta, yellow and black from the nozzles in one way movement of the print head in the main scanning direction. That is, the plurality of main scanning lines for one line printing are the lines of different colors.
In order to increase the printing speed in the serial scanning type ink jet printer or color ink jet printer, the numbers of the main scanning lines, which perform imaging or color imaging upon a single main scanning operation of the print head, must be increased. To this effect, an elongated print head has been used where arranged are nozzle cells each formed with greater numbers of nozzle holes.
Further, in case of a high speed ink jet printer, an elongated line print head is used. Such elongated head has nozzle cells arranged on approximately full width of the continuous sheet, each nozzle cells being formed with necessary numbers of nozzles corresponding to necessary numbers of main scanning lines.
In order to provide the elongated print head, multiple nozzle cells are formed in a row extending in the line direction. In case of the color print head, rows of nozzle cells for different colors extends in the line direction and are arrayed side by side. However, such arrangement may lower productivity. Further, if only one of the nozzle cells may exhibit instable ink ejecting characteristic among multiple nozzle cells, the entire print head may lead to degradation in printing quality.
Another proposal is made to realize the elongated print head in which short length print head modules produced at high productivity are arrayed as disclosed in Japanese Patent publication No. Hei 3-5992. In case of the color printing, the arrays for different colors are provided side by side in the main scanning direction. The short length print head module provides high yieldability or productivity, and therefore, the combination of the short length print head modules can reduce production cost. However, this provide disadvantages as follows:
As shown in FIG. 4(a), a subordinate print head modules S are arranged in alternating staggered fashion in order to realize continuity of the nozzle holes in the auxiliary scanning direction of the resultant print head 510. Each subordinate print head module S includes a plurality of linear print head modules 1 arrayed side by side in the main scanning direction of the print head 510, and a distance between the neighboring subordinate print head modules S in the main scanning direction is greater than a width of the subordinate print head module S in the main scanning direction. Of course, instead of the subordinate print head modules S, the print head modules 1 can be arranged in alternating staggered fashion. However, in the latter case, the printing resolution may be dependent on the nozzle pitch of the print head module 1, or the resolution may be lower than a resolution estimated by the nozzle pitch. Accordingly, in order to provide high printing resolution, the above described subordinate print head modules S shown in FIG. 4(a) should be used, and these should be arrayed in the staggered fashion.
Similarly, in case of printing with two colors, as shown in FIG. 14(a), the above described subordinate print head modules S' are arrayed in the staggered fashion in a manner similar to the arrangement shown in FIG. 4(a), except that ink color of a first staggered array Si extending in the auxiliary scanning direction is different from an ink color of a second staggered array S2.
However, such staggered arrangement of the subordinate print head modules S or S', a width "Lj" of the print head in the main scanning direction is inevitably increased, and accordingly, nozzle array length in the main scanning direction is also increased. In particular, in case of a print head for four color printing, the four staggered arrays are required for four colors, and as a result, width "Lj" of the print head is more increased.
Thus, dot landing or impinging point on the continuous sheet may be varied due to variation in relative moving speed between the continuous sheet and the print head 510.
Specifically, in order to obtain high resolution print head 510, the subordinate print head module S must include a greater numbers of print head modules 1. Accordingly, the width of the subordinate print head module S in the main scanning direction must also be increased. Consequently, resultant width "Lj" in the main scanning direction of the print head 510 is increased to further increase nozzle array length in the main scanning direction. Thus, the problem of variation in dot landing point on the sheet becomes more serious.
Further, in addition to the above described problem of variation in dot landing point, the print head having increased nozzle array length in the main scanning direction provides another problem in terms of printing speed. The latter problem is particularly brought into attention in the serial scanning type printer.
That is, if the printing is to be performed to a position close to the widthwise end portions of the sheet by the serial scanning type printer having increased nozzle array length in the main scanning direction, the main scanning distance must be increased by the increased nozzle array length. More specifically, if the nozzle array length in the main scanning direction is increased, a leading end nozzle must be shifted largely out of the printing region in order to position a trailing end nozzle at the widthwise end portion of the sheet.